Sous Vide-Inspired Impregnation of Amorphous Titanium (Hydr)Oxide into Carbon Block Point-of-Use Filters for Arsenic Removal from Water.

Carbon block filters, commonly employed as point-of-use (POU) water treatment components, effectively eliminate pathogens and adsorb undesirable tastes, odors, and organic contaminants, all while producing no water waste. However, they lack the capability to remove arsenic. Enabling the carbon block to remove arsenic could reduce its exposure risks in tap water. Inspired by Sous vide cooking techniques, we developed a low-energy, low-chemical method for impregnating commercially available carbon block with titanium (hydr)oxide (THO) in four integrated steps: (1) vacuum removal of air from the carbon block, (2) impregnation with precursors in a flexible pouch, (3) sealing to prevent oxygen intrusion, and (4) heating in a water bath at 80 °C for 20 h to eliminate exposure and reactions with air. This process achieved a uniform 13 wt % Ti loading in the carbon block. Our modified carbon block POU filter efficiently removed both arsenate and arsenite from tap water matrices containing 10 or 100 µg/L arsenic concentrations in batch experiments or continuous flow operations. Surprisingly, the THO-modified carbon block removed arsenite better than arsenate. This innovative method, using 70% fewer chemicals than traditional autoclave techniques, offers a cost-effective solution to reduce exposure to arsenic and lower its overall risk in tap water.

Phenotypic and Transcriptional Responses of Pseudomonas aeruginosa Biofilms to UV-C Irradiation via Side-Emitting Optical Fibers: Implications for Biofouling Control.

Biofilms give rise to a range of issues, spanning from harboring pathogens to accelerating microbial-induced corrosion in pressurized water systems. Introducing germicidal UV-C (200-280 nm) irradiation from light-emitting diodes (LEDs) into flexible side-emitting optical fibers (SEOFs) presents a novel light delivery method to inhibit the accumulation of biofilms on surfaces found in small-diameter tubing or other intricate geometries. This work used surfaces fully submerged in flowing water that contained Pseudomonas aeruginosa, an opportunistic pathogen commonly found in water system biofilms. A SEOF delivered a UV-C gradient to the surface for biofilm inhibition. Biofilm growth over time was monitored in situ using optical conference tomography. Biofilm formation was effectively inhibited when the 275 nm UV-C irradiance was ≥8 µW/cm2. Biofilm samples were collected from several regions on the surface, representing low and high UV-C irradiance. RNA sequencing of these samples revealed that high UV-C irradiance inhibited the expression of functional genes related to energy metabolism, DNA repair, quorum sensing, polysaccharide production, and mobility. However, insufficient sublethal UV-C exposure led to upregulation genes for SOS response and quorum sensing as survival strategies against the UV-C stress. These results underscore the need to maintain minimum UV-C exposure on surfaces to effectively inhibit biofilm formation in water systems.

Increasing net water recovery of reverse osmosis with membrane distillation using natural thermal differentials between brine and co-located water sources: Impacts at large reclamation facilities.

Maximizing water recovery and minimizing the volume of RO concentrate (i.e., brine) produced is a growing challenge, especially for inland communities that lack ocean disposal options. In such regions, transitioning towards zero liquid discharge (ZLD) can avoid detrimental impacts associated with salt disposal via regional sewer discharge or deep-well injection. On-site ZLD energy requirements are proportional to the RO brine flowrate. Thus, system-level strategies that reduce RO brine flows will lower ZLD costs while simultaneously increasing the overall water recovery for beneficial reuse in reclamation facilities. We investigated a membrane distillation (MD) system operating using co-located, cooler source water to treat warmer wastewater RO brine. Using experimentally-quantified MD fluxes based on observed monthly water temperatures of co-located water and RO brine at a facility in central Arizona, and based on the previously reported performance of large-scale MD systems, energy consumption and operating cost were estimated to evaluate the potential capabilities of MD to treat RO brine at full scale facilities. When the RO unit was combined with MD brine treatment, net water recovery at the full-scale facility can increase from 85% to up to 91% while brine flow can be reduced by 26%. A 25% lower thermal energy was required to achieve RO net water recovery of 95% when using co-located water, compared against conventional MD without using co-located water. Overall, this work demonstrates the potential to use local thermal gradients to reduce RO brine volumes, thereby reducing ZLD costs.

Germicidal Ultraviolet Light Does Not Damage or Impede Performance of N95 Masks Upon Multiple Uses.

The COVID-19 pandemic is increasing the need for personal protective equipment (PPE) worldwide, including the demand for facial masks used by healthcare workers. Disinfecting and reusing these masks may offer benefits in the short term to meet urgent demand. Germicidal ultraviolet light provides a nonchemical, easily deployable technology capable of achieving inactivation of H1N1 virus on masks. Working with N95-rated masks and nonrated surgical masks, we demonstrated that neither 254 nor 265 nm UV-C irradiation at 1 and 10 J/cm2 had adverse effects on the masks' ability to remove aerosolized virus-sized particles. Additional testing showed no change in polymer structure, morphology, or surface hydrophobicity for multiple layers in the masks and no change in pressure drop or tensile strength of the mask materials. Results were similar when applying 254 nm low-pressure UV lamps and 265 nm light-emitting diodes. On the basis of the input from healthcare workers and our findings, a treatment system and operational manual were prepared to enable treatment and reuse of N95 facial masks. Knowledge gained during this study can inform techno-economic analyses for treating and reusing masks or lifecycle assessments of options to reduce the enormous waste production of single-use PPE used in the healthcare system, especially during pandemics.

Four release tests exhibit variable silver stability from nanoparticle-modified reverse osmosis membranes.

Modification of polyamide reverse osmosis (RO) membranes with silver nanoparticles (AgNP) may effectively control biofouling. While silver leaching tests are usually performed during membrane development, the lack of common testing protocols limits cross-comparison among different labs. We compare four release tests to quantify the release of dissolved and nanoparticulate silver from polyamide RO membranes prepared through in situ surface functionalization: (1) batch immersion, (2) dead-end filtration, (3) cross-flow filtration, and (4) low-pressure water jetting. For the first time, we demonstrated the possibility of AgNP release to membrane-treated water through direct AgNP detachment. When using Nanopure water as an extraction solution, water jetting resulted in the fastest silver mass release, while dead-end filtration caused the slowest release based on the initial release kinetic data. Dead-end filtration exhibited silver mass release an order of magnitude lower than the other three tests. Although cross-flow filtration may best represent the RO membrane operation, quantifying silver release suffers from poor mass balance due to the adsorption of dissolved silver by various reactor components and large volumes of water usage. A commonly applied batch immersion method was low cost and easily performed, but may not induce hydraulic shear sufficient for AgNP detachment from a RO membrane. The information on silver release behavior may depend on the specific test, which is important for assessing antimicrobial efficacy and service life of the nanoparticle-functionalized membranes.

Coupling Light Emitting Diodes with Photocatalyst-Coated Optical Fibers Improves Quantum Yield of Pollutant Oxidation.

A photocatalyst-coated optical fiber was coupled with a 318 nm ultraviolet-A light emitting diode, which activated the photocatalysts by interfacial photon-electron excitation while minimizing photonic energy losses due to conventional photocatalytic barriers. The light delivery mechanism was explored via modeling of evanescent wave energy produced upon total internal reflection and photon refraction into the TiO2 surface coating. This work explores aqueous phase LED-irradiated optical fibers for treating organic pollutants and for the first time proposes a dual-mechanistic approach to light delivery and photocatalytic performance. Degradation of a probe organic pollutant was evaluated as a function of optical fiber coating thickness, fiber length, and photocatalyst attachment method and compared against the performance of an equivalent catalyst mass in a completely mixed slurry reactor. Measured and simulated photon fluence through the optical fibers decreased as a function of fiber length, coating thickness, or TiO2 mass externally coated on the fiber. Thinner TiO2 coatings achieved faster pollutant removal rates from solution, and dip coating performed better than sol-gel attachment methods. TiO2 attached to optical fibers achieved a 5-fold higher quantum yield compared against an equivalent mass of TiO2 suspended in a slurry solution.

Transparent exopolymer particles (TEP) removal efficiency by a combination of coagulation and ultrafiltration to minimize SWRO membrane fouling.

This study investigated the impact of coagulation on the transformation between colloidal and particulate transparent exopolymer particles (TEP) in seawater; and the effectiveness of a combined pretreatment consisting of coagulation and UF on minimizing TEP fouling of seawater reverse osmosis (SWRO) membranes. Coagulation with ferric chloride at pH 5 substantially transformed colloidal TEP (0.1-0.4) into particulate TEP (>0.4) leading to a better membrane fouling control. Both 50 and 100 kDa molecular weight cut-off (MWCO) UF membranes removed most of particulate and colloidal TEP without the assistance of coagulation, but coagulation is still necessary for better UF fouling control. The improvement of combined SWRO pretreatment with coagulation and 50 kDa UF membranes was not that much significant compared to UF pretreatment with 50 KDa alone. Therefore, the minimal coagulant dosage for seawater containing TEP should be based on the UF fouling control requirements rather than removal efficiency.

Determining the effectiveness of conventional and alternative coagulants through effective characterization schemes.

Polymeric forms of metal coagulants in water treatment have become increasingly used due to their wider availability and reduction in cost. These specialized coagulant forms and products are claimed by manufacturers to be superior to conventional coagulants in particulate and/or organic removal with inherent advantages of lower alkalinity consumption and lesser sludge production. However, due to their proprietary nature, little is known about their chemical composition. To determine and understand the effectiveness of these alternative coagulants, a comprehensive study was undertaken to characterize metal coagulants, and to comparatively evaluate them on a well-characterized source water. The objective of this study was to provide a scheme for utilities that could be employed as a screening process and a method of selecting an appropriate coagulant based on raw water characteristics and insight into the coagulatability of the source water. Characterizations of coagulants included: (i) active metal content, (ii) anion content, (iii) acidity, (iv) alkalinity consumption, (v) charge reversal by colloidal titration, and (vi) molecular weight determination. A total of five poly-aluminum chlorides (PACl), along with a conventional coagulant (aluminum sulfate or alum) were evaluated. Results show that through the characterization scheme, an effective coagulant (conventional versus alternative) and coagulant type (among various PACl) can be chosen before undertaking time-consuming bench or pilot-scale evaluation.